TL;DR — Rate Limiter Service

Design a distributed rate limiter service that API gateways and microservices use to enforce request limits. The system must support multiple rate limiting algorithms (token bucket, sliding window, fixed window), work across a distributed fleet of API servers, and handle millions of rate limit checks per second with microsecond latency. Key features: Check if a request should be allowed or throttled based on configured limits. Support rate limiting by API key, user ID, IP address, or custom key.